Heavy metal and organic contamination of soils, buildings and equipment systems is a major environmental concern at both industrial and government sites. The contamination is primarily due to improperly disposed industrial wastes. The presence of toxic heavy metal ions, volatile organic compounds and pesticides in the environment is of great concern and could affect worker safety as well as the safety of drinking water and air for the general public.
Federal and state pollution control standards for heavy metal content of mineral-producing discharges and for other types of waste disposal have become increasingly stringent. In addition, acid mine runoff contaminated with dissolved metals from abandoned mines contributes to environmental degradation. Other sources of contamination include discharge from federal facilities, e.g., military weapons complexes, which are a source of metals, organics, and radionuclides. Additional sources of contamination include oil and gas exploration and production operations. Where dissolved metals must be removed from such a waste stream prior to discharge, precipitation is the most common method, generally precipitating the metals by adding calcium oxide. Although calcium oxide addition is relatively simple and cheap, this method results in a great volume of sludge which is costly and hazardous to dispose of. Moreover, because of incomplete reaction, the effluent is often not completely removed from the water, and the metal values are not recovered and are thereby wasted. Also, the precipitation layer in settling ponds undergoes an inversion at temperatures around 4.degree. C.
Many waters are contaminated with mixed wastes, which conventionally are treated with activated carbon followed by elution through ion exchange resin columns. Because these two methods operate on different principles, both technologies are applied sequentially, rather than simultaneously. This conventional technology is very expensive and cumbersome to use.
In Bureau of Mines Report of Investigations, 9200, Pahlman et al. describe the use of lignochemicals and humic acids to remove heavy metals from process waste streams. The sodium salt of lignin and the humic acids of peat, lignite, and subbituminous coal were found to be excellent at removing the more toxic heavy metal ions, including Cd.sup.+2, Pb.sup.+2 and Hg.sup.+2, while calcium oxide addition was found to be poor to fair for their removal. However, the coagulability of the heavy metal sequestrates of the lignin sodium salt at pH 7 makes removal less efficient and causes difficulty in filtration.
Pahlman et al. found that a mixture of three humic acids has a particular affinity for Cd.sup.+2, Hg.sup.+2 and Pb+2, and can be used to effect almost total removal of these ions from waste streams. The humic acids used were prepared by caustic treatment of a North Dakota lignite, a Montana subbituminous coal, and a Minnesota peat.
Alexander, in U.S. Pat. No. 5,034,045, describes a method for improving agricultural crop yields using a mixture of a water-soluble alkali metal salt of humic acid and plant nutrient components such as nitrogen, potassium, and/or phosphorus. In this case, the oxidized sites of humic acid are filled with non-volatile alkali metal ions that maintain the water solubility of the humate salt used.
Moran, in U.S. Pat. No. 4,459,149, discloses a process for treating humus materials comprising freeing humic acid from the combined state in which it frequently exists in humus materials, dispersing it as a fine, insoluble solid in acid process water, separating it from the impurities with which it is associated, and recovering it as a high solids filter cake. The humic acid can be solubilized by mixing with solubilizing agent such as alkaline salts and the like. Insoluble humates are obtained by adding a metal compound to a humate solution.
Muir, in U.S. Pat. No. 4,952,229, discloses a soil and foliar supplement for plants comprising a quantity of specific microbes and an organic acid such as humic acid, fulvic acid and ulvic acid, along with optional trace minerals and chelated micronutrients.
Although activated carbon is very effective in removing organic compounds, it is associated with high capital and operating costs, especially when regeneration is effected by the most effective process, thermal reactivation. Also, this technique is very sensitive to the presence of suspended solids, oil and grease, requiring pretreatment for effective performance.
Although conventional means for decontaminating surface and groundwater include a broad spectrum of treatment options such as precipitation, ion-exchange, microbial digestion, membrane separation, activated carbon absorption, etc., the state of the art technologies can in one pass remediate only one class of contaminants, i.e., either volatile organic compounds using activated carbon or heavy metals using ion exchange. This requires the use of at least two different stepwise processes to remediate a site.